Sensing method for wheel rotation, wheel localization method, and wheel localization system

ABSTRACT

A method of sensing wheel rotation can include: sensing magnetic force information in an environment of a wheel by a magnetometer to obtain measured magnetic force information; generating relative magnetic force information by performing mathematical operation processing in accordance with the measured magnetic force information, where the relative magnetic force information does not change with geomagnetic field and does change with a rotation angle of a wheel; and obtaining angle information related to the rotation angle of the wheel in accordance with the relative magnetic force information.

RELATED APPLICATIONS

This application claims the benefit of Chinese Patent Application No.201811196246.5, filed on Oct. 15, 2018, which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of automotiveelectronics technology, and more particularly to sensing methods forwheel rotation, wheel localization methods, and wheel localizationsystems.

BACKGROUND

Tire pressure monitoring systems (TPMS) can be used to monitor thestatus of tires by recording the tire speed or by use of electronicsensors in the tires, in order to provide effective safety for thedriving of motor vehicles. In one approach, an indirect tire pressuremonitoring system can be used to determine whether the tire pressure isnormal by the rotating speed difference. In another approach, a directtire pressure monitoring system can utilize air pressure monitoring andtemperature sensors in the tires. The air pressure and temperature ofthe tires may be monitored when the motor vehicles are driving orstationary. Alarms may go off when the tires are in a dangerous state(e.g., high pressure, low pressure, high temperature, etc.), in order toavoid potential traffic accidents caused thereby.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a waveform diagram of an example change relationship ofmeasurements of a Z-axis gravity acceleration meter with wheel rotation.

FIG. 2 is a waveform diagram of an example change relationship ofmeasurements of a Z-axis gravity acceleration meter with the wheelrotation and wheel speed.

FIG. 3 is a waveform diagram of an example change relationship of themeasurements of the Z-axis gravity acceleration meter with wheelrotation and wheel speed when the road is not flat.

FIG. 4 is waveform diagram of an example change relationship of relativemagnetic force information with wheel rotation, in accordance withembodiments of the present invention.

FIG. 5 is a waveform diagram of an example relationship of the wheelrotation angles at different time points calculated according to thechange of the relative magnetic force information, in accordance withembodiments of the present invention.

FIG. 6 is a waveform diagram of an example relationship of the wheelrotation angles at different time points obtained in accordance withembodiments of the present invention.

FIG. 7 is a schematic block diagram of an example wheel localizationsystem, in accordance with embodiments of the present invention.

FIG. 8 is a schematic block diagram of an example tire pressuremeasurement system, in accordance with embodiments of the presentinvention.

DETAILED DESCRIPTION

Reference may now be made in detail to particular embodiments of theinvention, examples of which are illustrated in the accompanyingdrawings. While the invention may be described in conjunction with thepreferred embodiments, it may be understood that they are not intendedto limit the invention to these embodiments. On the contrary, theinvention is intended to cover alternatives, modifications andequivalents that may be included within the spirit and scope of theinvention as defined by the appended claims. Furthermore, in thefollowing detailed description of the present invention, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. However, it may be readilyapparent to one skilled in the art that the present invention may bepracticed without these specific details. In other instances, well-knownmethods, procedures, processes, components, structures, and circuitshave not been described in detail so as not to unnecessarily obscureaspects of the present invention.

A tire pressure monitoring system (TPMS) may be used to monitor tirepressure and maintain proper pressure, which can play an important rolein ensuring the driving safety of vehicles. In a tire pressuremonitoring system, a sensor for detecting the tire pressure may beplaced in the tire, in order to transmit the detected tire pressure tothe vehicle's data processor for monitoring and prompting. The TPMS canmonitor pressure information of the tires through a tire pressure sensor(TPS) installed in the tires, and may report the pressure information tothe vehicle driver. Since the vehicle usually has a plurality of tires,TPMS may also have an automatic localization function to inform thedriver of which tire from which the pressure information is currentlyreceived.

One approach for automatic localization can include use of an angularposition sensing (APS), which can enable the TPMS to calculate therotation angle information of the wheel in which the TPS is installedbased on a set of measurements of the measured acceleration receivedfrom the TPS. Then, the rotation angle information obtained bycalculation of the APS may be compared against the wheel rotationderived from the sensor in the anti-lock brake system (ABS) of thevehicle, in order to obtain the location information of the wheel. OneAPS approach may utilize a gravity acceleration signal obtained by agravity acceleration sensor installed on the wheel to calculate andobtain rotation angle information of the wheel.

Referring now to FIG. 1, shown is a waveform diagram of an examplechange relationship of measurements of a Z-axis gravity accelerationmeter with wheel rotation. In this example, the measurement center valueof the Z-axis gravity acceleration sensor is 30g, where “g” is thegravitational acceleration. Also, the change value may be between −1gand +1g when only considering the change of the measurements caused bythe wheel rotation. When the TPMS rotates to position A directly belowthe wheel, the acceleration may be −1g due to its own gravity, and thecorresponding measurement is 29g. Similarly, when the TPMS is turned toposition B directly above the wheel, the acceleration can be +1g due toits own gravity, and the corresponding measurement may be 31g. When theTPMS is turned to position C directly in the middle of the wheel, thecorresponding acceleration may be just 30g. Thus, it can be seen thatthe wheel rotation information may be obtained through agravity-accelerated vehicle.

Referring now to FIG. 2, shown is a waveform diagram of an examplechange relationship of measurements of a Z-axis gravity accelerationmeter with wheel rotation and wheel speed. The average value measured inthe acceleration measurement system (e.g., the value when the TPMS is inthe middle of the wheel) can change with the change of vehicle speed.Therefore, in order to obtain more accurate wheel rotation angleinformation, the measurement frequency of acceleration can be greaterthan 4 times the wheel rotation period, which may result in greaterpower consumption.

Referring now to FIG. 3, shown is a waveform diagram of an examplechange relationship of measurements of a Z-axis gravity accelerationmeter with wheel rotation and wheel speed when the road is not flat.When the wheels rotate, vibrations may be generated due to differentflatness of the surface of the road. Thus, noise may be added to themeasurement result of the gravity acceleration sensor, as shown. Thiscan make the wheel rotation information calculated by measurements ofthe gravity acceleration sensor less accurate, such that accurateautomatic localization of the TPMS may not be realized. In someapproaches, a gravity acceleration sensor can be used to sense arotation angle of a wheel by sensing a change of a gravity accelerationcaused by wheel rotation. However, such an approach may have relativelyhigh power consumption and low accuracy.

In one embodiment, a method of sensing wheel rotation can include: (i)sensing magnetic force information in an environment of a wheel by amagnetometer to obtain measured magnetic force information; (ii)generating relative magnetic force information by performingmathematical operation processing in accordance with the measuredmagnetic force information, where the relative magnetic forceinformation does not change with geomagnetic field and does change witha rotation angle of a wheel; and (iii) obtaining angle informationrelated to the rotation angle of the wheel in accordance with therelative magnetic force information.

In certain embodiments, a sensing method can include arranging amagnetometer is arranged in the wheel. The measured magnetic forceinformation sensed by the magnetometer can be transmitted to anelectronic control unit. The electronic control unit can performmathematical operation processing on the received measured magneticforce information to generate relative magnetic force information thatdoes not change with geomagnetic field, but rather changes with therotation angle of the wheel. Then, the electronic control unit canobtain angle information related to the rotation angle of the wheelbetween a first and second time points according to the change amount ofthe relative magnetic force information between the first and secondtime points.

For example, the magnetometer described may be any suitable magneticsensor (e.g., a tunnel magneto resistance [TMR] sensor, a giant magnetoresistance [GMR] sensor, an anisotropic magneto resistance [AMR] sensor,a colossal magneto resistance [CMR] sensor, etc.). For example, afterthe magnetometer is arranged in the wheel, the measured magnetic forceinformation sensed by the magnetometer may include two parts. Forexample, one part is a geomagnetic component, which can change with themovement direction of the wheel (e.g., the wheel that goes forward indifferent directions), and the magnitude of the geomagnetic component inthe measured magnetic force information may accordingly change, thuscausing the change of the measured magnetic force information. Forexample, the other part is a magnetic force component generated by thevehicle itself with the wheel (e.g., generated by the engine and/or thevehicle body). The magnitude of the magnetic force may only be relatedto the relative position of the wheel and the vehicle (e.g., the angularposition of the wheel), independent of the movement direction and thespeed of the wheel. Thus, if the rotation of the wheel is directlysensed according to the change of the measured magnetic forceinformation (e.g., the rotation of the wheel refers to the angle atwhich the wheel rotates in a certain time), the accuracy may not berelatively high because the measured magnetic force information may notonly change with the rotation angle of the wheel, but also can relate tothe geomagnetic field.

In one example, after receiving the measured magnetic force information,the electronic control unit may not directly obtain angle informationrelated to the rotation angle of the wheel according to the change ofthe measured magnetic force information. Rather, the electronic controlunit may first perform mathematical operation processing on the receivedmeasured magnetic force information to obtain relative magnetic forceinformation that does not change with the geomagnetic field, but onlychanges with the rotation angle of the wheel. In this way, thegeomagnetic component in the relative magnetic force information may notchange with the movement direction of the wheel, such that the change ofthe relative magnetic force information may only be related to thechange of the rotation angle of the wheel.

Also, the rotation angle of the wheel during this period can beaccurately obtained according to the change amount of the relativemagnetic force information between the first and second time points. Theangle information can be directly the rotation angle of the wheelbetween the first and second time points; that is, the angular phasedifference of the wheel between the first and second time points. Ofcourse, the angle information can also be other parameters having aknown relationship with the rotation angle of the wheel; that is, therotation angle of the wheel between the first and second time points canbe clearly obtained through the angle information and the knownrelationship.

When the electronic control unit performs mathematical operationprocessing on the measured magnetic force information to obtain therelative magnetic force information, the mathematical operationprocessing can be relatively simple if the magnetometer is a triaxialmagnetometer. Therefore, in particular embodiments, the magnetometer canbe selected as a triaxial magnetometer (also referred to as a triaxialmagnetic sensor) with X-axis, Y-axis, and Z-axis. Accordingly, themeasured magnetic force information can include component X on theX-axis, component Y on the Y-axis, and component Z on the Z-axis. Theelectronic control unit may receive components X, Y, and Z, and mayperform mathematical operation processing on the three components toobtain the relative magnetic force information.

The mathematical operation can include respectively calculating thesquares of components X, Y, and Z, and adding the squares of componentsX, Y, and Z to obtain relative magnetic force information; that is, therelative magnetic force information is X²+Y²+Z². The relative magneticforce information may not change with the change of geomagnetic field;that is, it may not change with the change of wheel movement direction,but may only change with the change of wheel rotation angle. Therefore,the angle information related to the rotation angle of the wheelobtained according to the relative magnetic force information may have ahigher relative accuracy, and the measurement frequency may not need tobe more than four times the rotation period of the wheel, as well as notcausing increased power consumption.

The electronic control unit can initially fit the change relationship ofthe relative magnetic force information with the rotation angle of thewheel according to the change of the relative magnetic force and thecorresponding rotation angle of the wheel, and may save the relatedinformation of the change relationship. This process can be regarded ascorrection of the relative magnetic force information. In a subsequentprocess, the electronic control unit can quickly obtain thecorresponding change of the relative magnetic force informationaccording to the changes of components X, Y, and Z received each time,such that the rotation angle of the wheel can be quickly obtained withina certain time period.

Referring now to FIG. 4, shown is a waveform diagram of an examplechange relationship of relative magnetic force information with wheelrotation, in accordance with embodiments of the present invention. Timepoints T1 and T2 can be the “first” group of the first and second timepoints, where time point T1 is the “first” time point, and time point T2is the “second” time point. At time point T1, the wheel may rotate to afirst position, at which time the magnetometer fixedly installed in thewheel can be located directly above the wheel, and the correspondingmagnitude of the relative magnetic force information may be 1.3. Atsecond time point T2, the magnetometer can rotate to the middle positionof the wheel with the rotation of the wheel, and the correspondingmagnitude of the relative magnetic force information may be 0.8.

Thus in this example, it can be seen that from time point T1 to timepoint T2, the change amount of the relative magnetic force informationis 0.5, and the corresponding rotation angle of the wheel is 90°. Forthe “second” group of the first and second time points, time point T2 isthe “first” time point, and time point T3 is the “second” time point. Inthis particular example, from time point T2 to time point T3, the changeamount of the relative magnetic force information is 0.5, and thecorresponding rotation angle of the wheel is 90°. Therefore, any twotime points during the rotation of the wheel can form a group of thefirst and second time points, and the angle information of the wheelrotation between the two time points can be obtained according to thechange information of the relative magnetic force between the first andsecond time points.

In order to fit the change relationship of the relative magnetic forceinformation with the rotation angle of the wheel, the magnetometer cansend the measured magnetic force information to the electronic controlunit for many times (e.g., more than 20 times) continuously during theearly sensing period of the wheel rotation. The electronic control unitcan perform the mathematical operation process once each time themeasured magnetic force information is received, in order to obtain aplurality of the relative magnetic force information corresponding to aplurality of the measured magnetic force information. Then, theelectronic control unit can fit the change relationship of the relativemagnetic force information with the rotation angle of the wheelaccording to the change amount between the plurality of the relativemagnetic force information and the corresponding rotation angles of thewheel. After determining the change relationship, the electronic controlunit can receive the measured magnetic force information eachpredetermined time (e.g., every 30 seconds), then can obtain thecorresponding relative magnetic force information according to themeasured magnetic force information, and may obtain the angleinformation according to the change amount of the relative magneticforce information and the change relationship.

Particular embodiments can also include a method of localizing theposition of at least one of the plurality of wheels of a vehicle. In theexample localization method, angle information related to the rotationof the at least one wheel may be needed, and the angle information canbe obtained according to the example method for obtaining angleinformation by any one of the wheel rotation sensing methods providedherein. The example localization method can include determining angleinformation of the at least one wheel (e.g., a wheel to be localizedamong the plurality of wheels of the vehicle) according to the wheelrotation sensing method. In addition, the rotation position informationrelated to rotation positions of each of the plurality of wheels can beobtained from an ABS unit. Further, the respective rotation informationrelated to the rotation angle of each of the plurality of wheels betweenthe first and second time points can be obtained according to therotation position information. In addition, a position of the at leastone wheel in the vehicle may be determined according to the comparisonbetween the angle information and the corresponding rotationinformation.

For example, obtaining the rotation position information described caninclude obtaining a first rotation position information related to therotation positions of each of the plurality of wheels from the ABS unitat the first time point, and obtaining a second rotation positioninformation related to the rotation positions of each of the pluralityof wheels from the ABS unit at the second time point. For example, theelectronic control unit may be electronic control unit TPMS_ECU (see,e.g., FIGS. 7 and 8) in the TPMS of the vehicle. Also for example, thefirst and second rotation position information may be directlytransmitted to electronic control unit TPMS_ECU, and electronic controlunit TPMS_ECU can execute the appropriate command (e.g., calculating thedifference between the first and second rotation position information toobtain the rotation information). In another example, the first andsecond rotation position information may be initially transmitted toanti-lock brake system control unit ABS_ECU in ABS unit of the vehicle,and anti-lock brake system control unit ABS_ECU may execute theappropriate command (e.g., calculating the difference between the firstand second rotation position information to obtain the rotationinformation). In some examples, the appropriate command can be executedby electronic control unit TPMS_ECU.

Particular embodiments can also include estimating each estimatedrotation angle of each of the plurality of wheels between the first andsecond time points, according to the rotation information, comparing theestimated rotation angle against a calculated rotation angle of the atleast one wheel between the first and second time points obtained basedon the angle information, and determining the position of the at leastone wheel by matching a corresponding one of the estimated rotationangles with the calculated rotation angle according to the comparisonresult. In order to accurately localize the position of the at least onewheel, the position of the at least one wheel in the vehicle can bedetermined according to two or more groups of comparison results betweenthe calculated rotation angle and each of the estimated rotation angles.

Referring now to FIG. 5, shown is a waveform diagram of an examplerelationship between a calculated rotation angle of the wheel atdifferent time points and the relative magnetic force information, inaccordance with embodiments of the present invention. Referring also toFIG. 6, shown is a waveform diagram of example relationship betweenestimated rotation angles of the wheels at different time points androtation information, in accordance with embodiments of the presentinvention. Time points T1 and T2 may form a first group of the first andsecond time points, where time point T1 is the first time point, andtime point T2 is the second time point. Time points T2 and T3 may form asecond group of the first and second time points, where time point T2 isthe first time point and time point T3 is the second time point. Asshown in FIG. 5, the first set of the calculated rotation anglecorresponding to the first group of the first and second time points is100°, and the second set of calculated rotation angle corresponding tothe second group of first and second time points is −160°.

In addition, each of the rotation information can be “teeth” countinformation on the change number of the wheel teeth rotatedcorresponding to one of the wheels between the first and second timepoints. The first rotation position information may be the first teethnumber for the number of wheel teeth rotated corresponding to each ofthe wheels at the first time point, and the second rotation positioninformation can be the second teeth number for the number of wheel teethrotated corresponding to each of the wheels at the second time point. Asshown in FIG. 6, the plurality of wheels can include a right frontwheel, a left front wheel, a right rear wheel, and a left rear wheel. Inthe first group of first and second time points, at time point T1, therespective first teeth number corresponding to the right front wheel,the left front wheel, the right rear wheel, and the left rear wheel canbe 18, 27, 21, and 33, respectively. At time point T2, the respectivesecond teeth number corresponding to the right front wheel, the leftfront wheel, the right rear wheel, and the left rear wheel can be 15,30, 23, and 12, respectively. Then, estimated rotation angles in thefirst group corresponding to the right front wheel, the left frontwheel, the right rear wheel, and the left rear wheel can be 90°, 180°,138°, and 72°, respectively.

Thus, from the comparison between the first set of calculated rotationangle and the first group of estimated rotation angles in this example,it can be seen that the estimated rotation angle of the right frontwheel may be closest to the first set of calculated rotation angle, andthe at least one wheel can be determined to be the right front wheel ofthe vehicle. In order to further determine the result, further judgmentcan be made according to the comparison between the corresponding secondset of the calculated rotation angle and each of the estimated rotationangles in the second group of the first and second time points (e.g.,time points T2 and T3). In the second group of the first and second timepoints, at time point T2, the respective first teeth numbercorresponding to the right front wheel, the left front wheel, the rightrear wheel, and the left rear wheel can be 33, 57, 44, and 45,respectively. At time point T3, the respective second teeth numbercorresponding to the right front wheel, the left front wheel, the rightrear wheel, and the left rear wheel can be 4, 41, 22, and 10,respectively. Since the total change number of teeth in one turn of thewheel is 60 in this example, the total number of the teeth of each wheelis 60.

Then, in the second group of first and second time points, therespective second set of rotation information corresponding to the rightfront wheel, the left front wheel, the right rear wheel, and the leftrear wheel (that is, the second set of teeth number for the number ofthe teeth rotated) can be 31, 44, 38, and 25, respectively. Estimatedrotation angles in the second group corresponding to the right frontwheel, the left front wheel, the right rear wheel, and the left rearwheel can respectively be −174°, −96°, −132°, and −120°. Thus, from thecomparison between the second set of calculated rotation angle and thesecond group of estimated rotation angles, it can be seen that theestimated rotation angle of the right front wheel is still closest tothe second set of calculated rotation angle, and the at least one wheelcan be further determined to be the right front wheel of the vehicle.

In one embodiment, an apparatus for localizing at least one wheel of avehicle can include: (i) at least one magnetometer arranged in at leastone wheel, and being configured to obtain measured magnetic forceinformation; (ii) an ABS unit configured to provide rotation positioninformation related to rotation positions of each wheel; and (iii) anelectronic control unit configured to generate relative magnetic forceinformation in accordance with the measured magnetic force information,obtain angle information related to the rotation angle of the wheel inaccordance with the relative magnetic force information, obtain rotationinformation of the rotation angles of each wheel in accordance with therotation position information, and determine a position of the wheel inthe vehicle by comparing the angle information against each rotationinformation, where the relative magnetic force information does notchange with geomagnetic field and does change with a rotation angle of awheel.

Referring now to FIG. 7, shown is a schematic block diagram of anexample wheel localization system, in accordance with embodiments of thepresent invention. The system can localize the position of at least oneof a plurality of wheels of a vehicle. The localization system caninclude a magnetometer arranged in at least one wheel for sensing themeasured magnetic force information in the environment in which at leastone wheel is located. Here, the measured magnetic force information caninclude a geomagnetic component which changes with the movementdirection of at least one wheel and a magnetic force component generatedby the vehicle. The localization system may also include electroniccontrol unit TPMS_ECU, which can perform mathematical operationprocessing according to the received measured magnetic forceinformation, generating relative magnetic force information which maynot change with geomagnetic field but changes with the rotation angle ofat least one wheel, and obtaining angle information related to therotation angle of the wheel according to the change of the relativemagnetic force information between the first and second time points. Inaddition, the localization system can also include an ABS unit that canprovide the electronic control unit with rotation position informationrelated to the rotation position of each of the plurality of wheels. Theelectronic control unit can obtain each rotation information related tothe rotation angle of each wheel between the first and second timepoints based on the rotation position information, and can determine theposition of the at least one wheel in the vehicle according to thecomparison between the angle information and the corresponding rotationinformation.

Each of the plurality of wheels may need to be localized, and thus eachwheel of the vehicle may be provided with a magnetometer. Also, a tirepressure monitoring device can be provided for the wheel to monitor thetire pressure, and the magnetometer can be a part of the tire pressuremonitoring device. In this example, the tire pressure monitoring deviceshown in FIG. 7 can include the magnetometer described. For example,electronic control unit TPMS_ECU can form a TPMS of the vehicle togetherwith the tire pressure monitoring device. Electronic control unitTPMS_ECU can obtain the measured magnetic force information from themagnetometer through wireless or wired reception, and may furtherreceive the measured magnetic force information each predetermined time(e.g., 30 s), and may obtain the relative magnetic force informationaccording to the measured magnetic force information received each time.In addition, the localization system can also include a tire pressuresensor that can be arranged in the tire pressure monitoring device, andcan generate tire pressure information related to tire pressure of atleast one tire to electronic control unit TPMS_ECU. After determiningwhich wheel the tire pressure information comes from, electronic controlunit TPMS_ECU may transmit the identification name of the tire pressuresensor to the wheel.

The ABS unit can include rotation speed sensors installed in each wheelof the vehicle and control unit ABS_ECU. Each of the rotation speedsensors can obtain rotation speed sensing information related to therotation speed of the wheel teeth of each corresponding wheel. Controlunit ABS_ECU may obtain each of the corresponding rotation positioninformation according to each of the rotation speed sensing information,and can generate the rotation position information to electronic controlunit TPMS_ECU. For example, if the ABS unit provides the electroniccontrol unit with the first rotation position information related to therotation position of each wheel at the first time point, and the secondrotation position information related to the rotation position of eachwheel at the second time point, electronic control unit TPMS_ECU cancalculate the difference between the first and second rotation positioninformation to obtain the rotation information. Each of the rotationinformation can include teeth count information on the change number ofthe wheel teeth rotated corresponding to one of the wheels between thefirst and second time points. Thus, each of the first rotation positioninformation can be the first teeth number of the wheel teeth rotatedcorresponding to each wheel at the first time point (e.g., 18, 27, 21,and 33 in FIG. 6), and each of the second rotation position informationcan be second teeth number of the wheel teeth rotated corresponding toeach wheel at the second time point (e.g., 33, 57, 44, and 45 in FIG.6).

Electronic control unit TPMS_ECU can obtain the position of at least onewheel according to the calculation and comparison between the angleinformation and the respective rotation information according to theexemplified localization method. It should be understood that themagnetometer in the localization system can be an magnetometer asdescribed herein, and electronic control unit TPMS_ECU can be theelectronic control unit as described herein. As such, electronic controlunit TPMS_ECU can obtain the angle information according to the measuredmagnetic force information.

Referring now to FIG. 8, shown is a schematic block diagram of anexample tire pressure measurement system, in accordance with embodimentsof the present invention. The tire pressure measurement system caninclude magnetometers, tire pressure sensors, and electronic controlunit TPMS_ECU. The magnetometers can be arranged in at least one of aplurality of wheels of the vehicle, and may obtain measured magneticforce information in the environment in which the at least one wheel ispositioned. The tire pressure sensors can be arranged in at least one ofthe plurality of wheels of the vehicle, and may obtain tire pressureinformation related to the tire pressure of the at least one wheel.Electronic control unit TPMS_ECU can receive the measured magnetic forceinformation, tire pressure information, and rotation positioninformation related to rotation positions of each wheel provided by anABS unit of the wheel, in order to perform localization of the wheelaccording to the measured magnetic force information and the rotationposition information. Then electronic control unit TPMS_ECU can providean identification name of the tire pressure sensor to the wheel.

In particular embodiments, electronic control unit TPMS_ECU can performa mathematical operation on the measured magnetic force information toobtain relative magnetic force information which does not change withgeomagnetic field but changes with the rotation angle of the at leastone wheel, and may obtain angle information related to the rotationangle of the wheel between the first and second time points according tothe change amount of the relative magnetic force information between thefirst and second time points. Also, electronic control unit TPMS_ECU canobtain each of the rotation information related to the rotation angle ofeach of the plurality of wheels between the first and second time pointsaccording to the rotation position information, and may performlocalization of the wheel according to the comparison between the angleinformation and each of the rotation information.

In addition, the TPMS can include radio frequency unit RF for performingsignal transmission with electronic control unit TPMS_ECU, an antennaconnected to radio frequency unit RF, and a power supply unit forsupplying power to the system, such as battery. In combination with thedescription of the localization method and the localization systemprovided herein, the TPMS can realize tire pressure monitoring whileachieving automatic wheel localization. The electronic control unit canobtain the relative magnetic force that does not change with geomagneticfield through the mathematical operation processing on the measuredmagnetic force obtained by the magnetometer, and can obtain angleinformation and wheel position information according to the relativemagnetic force information. Since the relative magnetic forceinformation may not change with different directions of the wheelrotation, but only changes with the wheel rotation angle, the obtainedangle information and the position information may have relatively highaccuracy.

The embodiments were chosen and described in order to best explain theprinciples of the invention and its practical applications, to therebyenable others skilled in the art to best utilize the invention andvarious embodiments with modifications as are suited to particularuse(s) contemplated. It is intended that the scope of the invention bedefined by the claims appended hereto and their equivalents.

What is claimed is:
 1. A method of sensing wheel rotation, the methodcomprising: a) sensing magnetic force information in an environment of awheel by a magnetometer to obtain measured magnetic force information;b) generating relative magnetic force information by performingmathematical operation processing in accordance with the measuredmagnetic force information, wherein the relative magnetic forceinformation does not change with geomagnetic field and does change witha rotation angle of a wheel; and c) obtaining angle information relatedto the rotation angle of the wheel in accordance with the relativemagnetic force information.
 2. The method of claim 1, further comprisingobtaining the angle information related to the rotation angle of thewheel between a first time point and a second time point in accordancewith a change of the relative magnetic force information between thefirst and second time points.
 3. The method of claim 1, wherein: a) themagnetometer comprises a triaxial magnetometer; b) the measured magneticforce information comprises a first component on a first axis, a secondcomponent on a second axis, and a third component on a third axis; andc) the relative magnetic force information is obtained by performing themathematical operation processing based on the first, second, and thirdcomponents.
 4. The method of claim 3, wherein the mathematical operationprocessing comprises: a) respectively calculating squares of the first,second, and third components; and b) adding the square of the firstcomponent, the square of the second component, and the square of thethird component, to obtain the relative magnetic force information. 5.The method of claim 1, further comprising: a) performing themathematical operation processing each time after receiving the measuredmagnetic force information for a plurality of times continuously toobtain a plurality of corresponding relative magnetic force information;and b) fitting a change relationship of the relative magnetic forceinformation with the rotation angle of the wheel.
 6. The method of claim5, further comprising: a) receiving the measured magnetic forceinformation each predetermined time after the change relationship isdetermined to obtain the relative magnetic force information; and b)obtaining the angle information in accordance to a change of therelative magnetic force information and the change relationship.
 7. Amethod of wheel localization, comprising determining the angleinformation of the wheel in a vehicle in accordance with claim 1, themethod further comprising: a) obtaining rotation position information onrotation positions of each wheel from an anti-lock brake system (ABS)unit; b) obtaining rotation information of each wheel on the rotationangle in accordance with rotation position information; and c)performing wheel localization by comparing the angle information witheach of the rotation information correspondingly.
 8. The method of claim7, further comprising: a) obtaining the angle information on therotation angle of the wheel between a first time point and a second timepoint in accordance with a change of the relative magnetic forceinformation between the first and the second time points; and b)obtaining each rotation information on the rotation angles of each wheelbetween the first and the second time points in accordance with a changeof the rotation position information between the first and second timepoints.
 9. The method of claim 8, further comprising: a) obtaining firstrotation position information on rotation positions of each wheel at thefirst time point; b) obtaining second rotation position information onrotation positions of each wheel at the second time point; and c)obtaining the rotation information in accordance with a differencebetween the first and second rotation position information.
 10. Themethod of claim 7, further comprising: a) estimating an estimatedrotation angle of each wheel between a first time point and a secondtime point in accordance with the rotation information; b) comparingeach of the estimated rotation angles against a calculated rotationangle of the wheel obtained in accordance with the angle informationbetween the first and second time points; and c) performing localizationof the wheel in the vehicle in accordance with a comparison result thatan estimated rotation angle matches the calculated rotation angle. 11.The method of claim 10, further comprising determining the position ofthe wheel in the vehicle in accordance with more than two sets of thecomparison between the calculated rotation angle and each of theestimated rotation angles.
 12. The method of claim 8, wherein: a) eachof the rotation information is respectively teeth count information on achange number of wheel teeth rotated corresponding to of each wheelbetween the first and second time points; and b) the rotation positioninformation comprises the first teeth number of wheel teeth rotated ofeach wheel at the first time point, and the second teeth number of wheelteeth rotated of each wheel at the second time point.
 13. An apparatusfor localizing at least one wheel of a vehicle, the apparatuscomprising: a) at least one magnetometer arranged in at least one wheel,and being configured to obtain measured magnetic force information; b)an anti-lock brake system (ABS) unit configured to provide rotationposition information related to rotation positions of each wheel; and c)an electronic control unit configured to generate relative magneticforce information in accordance with the measured magnetic forceinformation, obtain angle information related to the rotation angle ofthe wheel in accordance with the relative magnetic force information,obtain rotation information of the rotation angles of each wheel inaccordance with the rotation position information, and determine aposition of the wheel in the vehicle by comparing the angle informationagainst each rotation information, wherein the relative magnetic forceinformation does not change with geomagnetic field and does change witha rotation angle of a wheel.
 14. The apparatus of claim 13, wherein theelectronic control unit is configured to: a) obtain the angleinformation on the rotation angle of the wheel between a first timepoint and a second time point in accordance with a change of therelative magnetic force information between the first and the secondtime points; and b) obtain rotation information on the rotation anglesof each wheel between the first and second time points in accordancewith a change of the rotation position information between the first andsecond time points.
 15. The apparatus of claim 13, wherein: a) themagnetometer comprises a triaxial magnetometer; b) the measured magneticforce information comprises a first component on a first axis, a secondcomponent on a second axis, and a third component on a third axis; andc) the electronic control unit is configured to perform a mathematicaloperation processing based on the first, second, and third components toobtain the relative magnetic force information.
 16. The apparatus ofclaim 15, wherein the mathematical operation processing comprises: a)respectively calculating squares of the first, second, and thirdcomponents; and b) adding the square of the first component, the squareof the second component, and the square of the third component, toobtain the relative magnetic force information.
 17. The apparatus ofclaim 13, wherein the electronic control unit is configured to perform amathematical operation processing each time after receiving each of aplurality of measured magnetic force information continuouslytransmitted by the magnetometer for a plurality times, in order toobtain a plurality of corresponding relative magnetic force information,and to fit a change relationship of the relative magnetic forceinformation with the rotation angle of the wheel.
 18. The apparatus ofclaim 17, wherein the electronic control unit is configured to receivethe measured magnetic force information each predetermined time afterthe change relationship is determined to obtain the relative magneticforce information, and obtain the angle information in accordance to achange of the relative magnetic force information and the changerelationship.
 19. The apparatus of claim 14, wherein the ABS unit isconfigured to provide first rotation position information on rotationpositions of each wheel at the first time point, and second rotationposition information on rotation positions of each wheel at the secondtime point for the electronic control unit, wherein the electroniccontrol unit is configured to obtain the rotation information inaccordance with a difference between the first and second rotationposition information.
 20. The apparatus of claim 14, wherein theelectronic control circuit is configured to estimate an estimatedrotation angle of each wheel between the first and second time points inaccordance with the rotation information, and to perform localization ofthe wheel by matching an estimated rotation angle to a calculatedrotation angle obtained in accordance with the angle information betweenthe first and second time points.